A report on CNN says that NASA is launching a spacecarft called the Deep Impact in mid-January. They plan to collide a part of the spacecraft call the "impactor" with Comet Tempel 1 on July 4, 2006. The collision is expected to blast a crater into the comet allowing Deep Impact to analyze the ice, dust and other primordial stuff that will be hurled out during the impact. The energy produced will be like 4.5 tons of TNT going off. The resulting pit -- anywhere from two to 14 stories deep -- will be just a dent by celestial standards.
Among other things scientists expect to learn something about deflecting a killer comet -- or possibly an asteroid -- if one ever comes Earth's way.